The present invention relates generally to multi-band antennas in wireless terminals, and more particularly to improving the performance of the multi-band antenna using a frequency band specific matching network.
Conventional wireless terminals typically include multi-band antenna systems that enable the wireless terminal to operate in multiple frequency bands. An exemplary multi-band antenna system may operate in a GSM band (824-894 MHz), an EGSM band (880-960 MHz), a PCS band (1850-1990 MHz) and/or a DCS band (1710-1880 MHz). Typically, a primary antenna of the multi-band antenna operates in two frequency bands—a low frequency band and a high frequency band.
When additional or wider frequency bands of operation are desired, the antenna system may further include a parasitic antenna element to expand the bandwidth of either the high or the low frequency bands or to add a third, separate frequency band. For example, a multi-band antenna with a primary antenna configured to operate in both the GSM and the PCS bands often includes a parasitic antenna tuned to the DCS frequency band. In this example, the parasitic antenna capacitively couples to the primary antenna. As a result, the parasitic antenna expands the bandwidth of the high frequency band to include both PCS and DCS frequencies. However, while the parasitic antenna generally expands the bandwidth of the high frequency band, the proximity of the parasitic antenna to the low frequency portion of the primary antenna may reduce the bandwidth of the low frequency band, and may also reduce the gain of the multi-band antenna system in the low frequency band.